Sorry, I couldn't read all 13 pages of messages and hope you got the advice you needed.
My own perspective is that I have four children, and I have a very different relationship with each of them. I have considered whether a couple of them should receive anything in my will, or at least as much as the others, given their treatment of and language used towards me and my partner.
But they are all my kids.
At the end of the day, I want to leave this world knowing I did what I could for all of them, including the s, and if they decide not to come to my funeral or to spend the lot on a massive party celebrating the fact that I am dead, that is their choice and nobody can put the blame on me.
I think the situation is different if said child is say a drug addict and giving them access to cash could be harmful but there are ways to deal with that (sorry if this has already been discussed, as I say I have not read the full thread). But otherwise, you're a long time dead, and this is one decision you cannot come back from when tempers calm down.
Has your DH also considered the potentially massive impact that this could have on DD1 that she may never recover from, given she will never be able to discuss it with him. To be told publicly how little you are loved would be traumatizing for most people, and would directly set her against her siblings that are clearly favoured, which could also destroy any relationship they could have in the future (endless resentment that their curtains/car/kid's school fees were paid for by money that should have been hers......).
It's up to him what he does with his money obviously, but unless there are major reasons underlying his decision I think this is a much bigger decision in terms of its potential consequences than perhaps he thinks.